1. Field of the Invention
The present invention relates to a method for automatically processing a plurality of sheets by means of printing and finishing on a printing system, the method comprising the steps of receiving printing instructions for printing the plurality of sheets, and receiving finishing instructions for finishing the plurality of sheets after printing in order to form a stack of printed and finished sheets, the stack having a stack height. The finishing instructions comprise an instruction to create a new target stack edge extending in a direction of the stack height at an intended position on each of the plurality of sheets, printing a mark on each sheet of a group of sheets out of the plurality of sheets, the mark intended to hit the new target stack edge in a group of at least one target hit point, and finishing the plurality of printed sheets according to the finishing instructions by creating a new actual stack edge. A target hit point is an intended intersection point of the mark with the new target stack edge. The new target stack edge may be an end grain of the stack.
The present invention further relates to a printing system configured to perform the method according to the present invention.
2. Description of the Background Art
A printing system may comprise a print engine for printing images on the plurality of sheets and a finishing module, in-line or off-line, for finishing the plurality of printed sheets. The plurality of printed sheets may form a stack of printed sheets of a certain height defined as the stack height. The plurality of printed sheets may also be offered to the finishing module in order to form a stack of printed sheets, which are then ready to be finished. The finishing instructions may be transferred from a control unit of the printing system to the finishing module directly, or via the print engine. The finishing module may be configured to trim the stack of printed sheets, to cut the stack of printed sheets, to drill the stack of printed sheets, to punch the stack of printed sheets, or to fold the stack of sheets. A trimming operation splits the stack into a part, which is waste, and a part, which is an end product or which is usable for further finishing operations. A cutting operation splits the stack into two parts, which are both usable for an end product or for a further finishing operation. The cutting operation may be performed using a die. A drilling operation creates a hole in the stack in the direction of the stack height, and a punching operation does the same. The created hole may have a circular circumference, or a rectangular circumference, or any other geometrical form. The trimming operation creates at least one new edge, including an edge at the place in the stack where the trimming actually happens, i.e. where a trim knife cuts the stack. The cutting operation creates at least one new edge, including an edge at the place where the stack is divided into at least two parts.
A drilling operation or a punching operation creates a new edge at the inside area of the hole, which may have a circular, rectangular or other geometrically shaped cross-section.
Trimming marks are known, which are printed on a sheet, to indicate the intended location of the trimming line. Cutting marks are known, which are printed on a sheet, to indicate the intended location of the cutting line. When the sheet has been trimmed or cut, the presence of the mark on an inner area of the trimmed or cut sheet indicates that the trimming or cutting was not at the right location. The presence of the mark on the edge of the trimmed or cut sheet indicates that the trimming or cutting was successful, and the absence of the mark on trimmed or cut sheet indicates that the trimming or cutting was also not at the right location. Usually the sheet at the top of the stack is well examined with respect to the marks. However, if a stack has a substantial stack height, a plurality of sheets needs to be examined and taken out of the stack. For example, a deviation or drift of a knife for cutting or trimming when the knife travels down through the stack may give rise to a different trimming or cutting behavior at the top sheets of the stack than at the bottom sheets of the stack.
Printing systems are known to print calibration marks on a top face of a sheet and a bottom face of the sheet, in order to correct for image-sheet registration, front-back registration and color correctness. Printing systems are also known to print cut or trim marks on a top sheet and/or a bottom sheet, to assist a process by a trimming device or a cutting device of the printing system, after printing the plurality of sheets by a print engine of the printing system. However, to produce a correctly finished end product, a trail-and-error method is usually applied, leading to a waste of sheets.